Conventionally, so-called self-monitoring of blood glucose (SMBG), in which blood drawn by puncturing a fingertip or the like by a dedicated puncture device is measured by a blood glucose meter each time blood is drawn, has been widely used as a method for a diabetic to measure and manage the blood glucose level for himself/herself.
As an alternative, a body fluid component measuring system allowing continuous glucose monitoring (CGM), in which the blood glucose level of a subject is continuously monitored with a sensor positioned indwelling in a skin by making a puncture under the skin or the like with a needle disposed on a dedicated sensor unit, has recently been developed (see Japanese Application Publication No. 2002-526137, for example), and has already been put to practical use in Europe and America.
The body fluid component measuring system used for CGM includes: a sensor unit mounted on a subject at all times; a transmitting unit for transmitting a measurement signal in the sensor unit to the outside, the transmitting unit being attached to the sensor unit; and a display device for calculating a blood glucose level on the basis of the measurement signal transmitted from the transmitting unit and displaying the blood glucose level. The sensor unit is replaced with a new sensor unit with a frequency of about once every few days to once every week.
The transmitting unit and the display device are used continuously irrespective of replacement of the sensor unit, and can be used for a long period of time by repeating the charging or replacement of batteries.
However, it is not desirable to interrupt the continuous monitoring of the blood glucose level of the subject for a long period of time each time the batteries included in the transmitting unit and the display device are charged or replaced. On the other hand, the cumulative value of time during which the continuous monitoring of the blood glucose level is interrupted can be reduced by decreasing the frequency of charging or the frequency of replacement of the batteries included in the transmitting unit and the display device. In that case, however, the batteries included in the transmitting unit and the display device are increased in size, thus decreasing the convenience of the subject that wears the transmitting unit and the display device at all times.